EP0490913B1 - Device for removably securing a tool to a machine spindle - Google Patents

Abstract

PCT No. PCT/EP90/01431 Sec. 371 Date Feb. 20, 1992 Sec. 102(e) Date Feb. 20, 1992 PCT Filed Aug. 28, 1990 PCT Pub. No. WO91/03346 PCT Pub. Date Mar. 21, 1991.The invention relates to a device for removably securing a tool (12) to the spindle (10) of a machine tool with a fitting aperture (16) concentric with the spindle axis, a fitting pin (18) engaging in the fitting aperture (16), two clamping bolts (26) arranged in the fitting pin so as to be radially movable towards opposite sides, a clamping member (32) movable axially by means of a tensioning mechanism fitted on the spindle side and two tapered surfaces (48, 30) fitted on the clamping member (32) on the one hand and on the clamping bolts on the other for the radial adjustment of the clamping bolts (26) between a release position withdrawn in the fitting pin (18) and a clamping position shifted radially outwards. In order to be able to clamp large tools securely, even with a relatively short axial clamping travel of the central securing and clamping mechanism on the spindle side, the clamping member (32) and the clamping bolts (26) each have a transverse groove therein (50, 52) limited by transverse sides in the region of their facing tapered surfaces (48, 30) by means of which the tapered surfaces are divided into two partial surfaces arranged at a distance from each other. In the release position, one of the partial surfaces (48'', 30') is received in the opposite transverse groove (50, 52) in the manner of a toothed gear, while in the clamping position both partial surfaces (30', 48', 30'', 48'') lie mutually opposite each other.

Description

The invention relates to a device for releasably connecting a tool to a spindle of a machine tool with a fitting hole concentric with the spindle axis, a fitting pin engaging in the fitting hole, at least one clamping bolt slidably mounted in the fitting pin in the radial direction, a clamping member axially displaceable by means of an adjusting mechanism arranged on the spindle side two wedge surfaces arranged on the clamping member on the one hand and on the clamping bolt on the other, inclined relative to the spindle axis, in pairs lying against each other for radially adjusting the clamping bolt between a release position retracted into the fitting pin and a radially outwardly displaced clamping position (US Pat. No. 4,684,301).

Connecting devices of this type are primarily intended for machine tools with automatic tool change, in particular for machining centers, with a central tool feed. This tool retraction, which is primarily intended for tool holding with a steep taper, works in most machining centers via a disc spring package with hydraulic expansion, whereby a head bolt arranged on the steep taper is pulled into the spindle by means of a pliers gripper while clamping the steep taper. The clamping distance required in the case of the steep taper coupling is approximately 6 to 10 mm depending on the size of the spindle. To for a given spindle size To achieve an increased rigidity compared to the steep taper connection, it has already been proposed to replace the steep taper seat by a cylindrical seat with end face support of the tool (magazine "Werkstatt und Betrieb" 119 (1986), pages 797 to 801) and at the same time that in many machine tools to use the existing central tool feed as a clamping mechanism.

In a known tool of the type specified, two radially displaceably mounted clamping bolts are therefore provided in the fitting pin, which can be moved diametrically outward via a clamping wedge, which is designed as a pulling wedge and can be moved axially via the spindle mechanism arranged on the spindle side. In their outwardly displaced clamping position, the clamping bolts engage with a truncated cone-shaped tip in a conical recess in the area of the bore wall of the receptacle in order to pull an annular flat surface adjacent to the fitting pin against a flat surface adjacent to the fitting bore and to brace it. In the release position, the clamping bolts are retracted so far into the fitting pin that the fitting pin can be pulled out of the fitting hole when the tool is changed. The clamping force that can be transmitted to the tool coupling for a given pull-in force of the central clamping mechanism is greater, the smaller the wedge angle of the wedge gear formed by the wedge surfaces of the clamping element and the clamping bolt. On the other hand, the wedge angle of the known tool coupling not be reduced arbitrarily, since this also reduces the radial stroke of the clamping bolts for a given axial adjustment path of the clamping mechanism. This disadvantage has an effect above all on larger tools which, in addition to an increased clamping force, also require a larger adjustment stroke of the clamping bolts. The known clamping mechanisms with disc spring assemblies can therefore not be easily used, especially with larger tools with flat surface bracing. Instead, hydraulic tool clamps have already been used, which allow a longer adjustment range. However, the costly retrofitting of machine tools and machining centers required for this limits the area of application for tools with flat surface bracing.

The invention is therefore based on the object of providing a connecting device of the type specified at the outset which, even with large tools, ensures reliable flat surface bracing with high clamping force and nevertheless manages with a relatively small axial clamping path of the spindle-side central pull-in and clamping mechanism.

To achieve this object, the combination of features specified in claim 1 is proposed. Further advantageous refinements and developments of the inventive concept result from the dependent claims.

The invention is based primarily on the idea that the major part of the stroke path for the almost force-free displacement of the clamping bolt from its retracted release position into the clamping position into its clamping position is necessary and that the actual clamping process requires only a very small stroke path. On the other hand, to ensure a torque-free power transmission, it must be ensured that the wedge surfaces bear against one another during the actual clamping process with a large base area. To achieve this, it is proposed according to the invention that the clamping member and the clamping bolt in the region of their mutually facing wedge surfaces have a transverse groove delimited by transverse flanks, through which the wedge surfaces are arranged in two spaced-apart positions, by one of the transverse flanks on the one hand and an outer one Transverse edge, on the other hand, limited partial areas are divided, that in the release position one of the partial areas engages in the opposite transverse groove in the manner of a toothing, that during the clamping process at least one of the transverse flanks and / or transverse edges abutting in pairs has a run-up slope that is steeper than the wedge slope relative to the spindle axis, and that in the clamping position the two partial surfaces bear against one another in pairs.

An optimal adaptation to a given clamping mechanism can also be achieved with large tools in that the wedge bevel in a range from 8 ° to 20 ° and the run-up slope is set in a range from 40 ° to 70 °.

In the finished state, the transverse grooves in the clamping bolt and in the tensioning member have an essentially trapezoidal cross section with flanks that diverge outwards. According to an advantageous embodiment of the invention, the run-up slope has a variable incline with respect to the spindle axis. For example, it can be convexly curved and, if necessary, pass smoothly and continuously into the wedge bevel.

In order to keep the tilting moment transmitted to the clamping bolt via the clamping element during the clamping process as small as possible, the transverse flank of the clamping bolt which is rotationally symmetrical on its outer surface and which strikes the clamping element during the clamping process is arranged near the axis of the clamping bolt. The transverse edge of the clamping bolt striking against the transverse flank of the clamping element during the clamping process is expediently at least single, preferably chamfered twice or convexly curved.

According to a preferred embodiment of the device according to the invention, in which the clamping bolt has two guide cheeks for the tensioning element which laterally delimit the wedge surfaces, the transverse groove of the clamping bolt is delimited at least at one end by one of the guide cheeks.

If the transverse groove is produced by the spark erosion process, the front-side boundary surfaces of the transverse groove protrude step-wise over the guide surfaces of the guide cheeks, while the clamping member has a corresponding material removal on its lateral guide surfaces in the area of the parts engaging in the transverse groove.

If, on the other hand, the transverse groove is designed as a milling groove, it can be introduced through a prefabricated elongated hole in one guide cheek, while on the side opposite the elongated hole, in the extension of the transverse groove, a blind hole with the contour of the transverse edge is formed from the inside into the relevant guide cheek can be. In this case, removal of material from the clamping element is not necessary.

In order to ensure adequate lubrication in the area of the wedge surfaces, the clamping bolt has a lubrication channel leading from its preferably cylindrical lateral surface to the wedge surface, the end of the lubrication channel on the wedge surface opening into the transverse groove.

The lubrication is preferably carried out through transverse bores which open into the transverse groove through the guide cheeks. A transverse bore opening into the transverse groove is advantageously arranged in each guide cheek, the transverse bores preferably engaging in and in the region of one of the transverse edges in each case a blind bore aligned with the transverse bore and open toward the transverse groove can be arranged on the opposite guide cheek. At least one of the transverse flanks can be formed by a part of the transverse bore surface that extends into the region of the wedge bevel. The latter is the case if the cross bores are also used as auxiliary bores in the manufacture of the cross groove in the milling process. The transverse groove base can then be aligned essentially perpendicular to the transverse bore axis. A centering hole coaxial to the clamping bolt axis and possibly cutting the run-up slope can be made in the transverse groove base as a production aid.

When changing the tool, the clamping bolt is automatically moved into its release position within the fitting pin by its conical tip when the clamping mechanism is released. Since the tool is gradually accelerated by the tool changer when the tool is removed, the force peaks acting on the clamping bolt are relatively small, so that a forced guidance of the clamping bolt via the clamping mechanism is not necessary. This consideration does not apply immediately to the assembly process, since there the fitting pin is inserted into the fitting hole at a relatively high speed and accordingly a protruding clamping bolt is subjected to high peak force. According to a preferred development of the invention, it is therefore proposed that the clamping bolt be releasably latched in its release position retracted into the fitting pin is. In the case of a device with a stop screw which is screwed into the fitting pin and engages with its tip in a groove of the clamping bolt which is closed at its ends, this can be accomplished in that the screw tip carries a locking ball which can be displaced against the force of a spring and which in the retracted release position of the clamping bolt is engaged in a locking recess arranged in the area of the groove base. The locking connection made in this way during the tool change between the clamping bolt and the fitting pin is released again during the clamping process using the clamping mechanism without great effort.

Fig. 1a

einen Schnitt durch eine Verbindungsvorrichtung zwischen einer Maschinenspindel und einem Werkzeug in Spannstellung;

Fig. 1b

einen Schnitt durch die Verbindungsvorrichtung in Freigabestellung;

Fig. 1c

eine Detailvergrößerung der Fig. 1a;

Fig. 2

einen Schnitt durch eine Rastvorrichtung für den Klemmbolzen;

Fig. 3

einen Klemmbolzen mit gefräster Quernut in schaubildlicher Darstellung;

Fig. 4

ein weiteres Ausführungsbeispiel eines Klemmbolzens mit gefräster Quernut in schaubildlicher Darstellung;

Fig. 5

eine Draufsicht auf den Klemmbolzen nach Fig. 4 in teilweise geschnittener Darstellung;

Fig. 6

einen Schnitt entlang der Schnittlinie 6-6 der Fig. 5;

Fig. 7

ein weiteres Ausführungsbeispiel eines Klemmbolzens mit gefräster Quernut und erodierter Auflaufschräge in schaubildlicher Darstellung;

Fig. 8

eine Draufsicht auf den Klemmbolzen nach Fig. 7;

Fig. 9

einen Schnitt entlang der Schnittline 9-9 der Fig. 8.

The invention is explained in more detail below with reference to an exemplary embodiment shown schematically in the drawing. Show it

Fig. 1a

a section through a connecting device between a machine spindle and a tool in the clamping position;

Fig. 1b

a section through the connecting device in the release position;

Fig. 1c

a detailed enlargement of Fig. 1a;

Fig. 2

a section through a locking device for the clamping bolt;

Fig. 3

a clamping bolt with milled transverse groove in a graphical representation;

Fig. 4

another embodiment of a clamping bolt with milled transverse groove in a diagrammatic Presentation;

Fig. 5

a plan view of the clamping bolt of Figure 4 in a partially sectioned representation.

Fig. 6

a section along the section line 6-6 of Fig. 5;

Fig. 7

a further embodiment of a clamping bolt with milled transverse groove and eroded run-up slope in a diagrammatic representation;

Fig. 8

a plan view of the clamping bolt of FIG. 7;

Fig. 9

7 shows a section along the section line 9-9 of FIG. 8.

As can be seen from FIGS. 1 a and b, a tool 12, for example a boring bar, not shown, can be exchangeably connected to a rotatably mounted spindle 10 of a machine tool, not shown, for example a machining center, by means of a connecting device 14. For this purpose, the spindle 10 has a fitting bore 16 concentric with the spindle axis, into which a cylindrical fitting pin 18 arranged on the tool can be axially inserted. In the tensioned state of the connecting device, the annular flat surface 20 which delimits the fitting bore 16 on the end face and the flat surface 22 surrounding the fitting pin at its root in an annular manner are pressed axially against one another. This flat surface bracing is caused by the coupling mechanism described below:

In a radial bore 24 of the fitting pin 18 are two diametrically opposed clamping bolts 26 mounted radially. The clamping bolts 26 have an essentially cylindrical lateral surface 27, a radially outwardly pointing frustoconical tip 28 and an inwardly facing wedge surface 30. Between the mutually facing wedge surfaces 30 of the two clamping bolts 26 there is a clamping member 32 designed as a double wedge, which is rigidly connected to a pull rod 34 which projects axially beyond the free end of the fitting pin 18 and is axially displaceable relative to the fitting pin. The pull rod 34 carries a coupling element 36 which can be gripped like a pliers by a spindle-side clamping mechanism, not shown in the drawing. A cavity 38 for receiving the clamping member 32 is arranged in the release position in the tool body 12. Screws 42 are screwed into the spindle 10 in the area of the fitting bore 16 into two diametrically opposed internal threads 40, which have radially inward-pointing conical recesses 44 for receiving the frustoconical tip 28 of the adjacent clamping bolt 26. If the pull rod 34 is axially displaced in the direction of arrow 46 by means of the tensioning mechanism (not shown), this displacement movement is implemented via the wedge-shaped tensioning element 32 into a radial stroke of the clamping bolts 26. The truncated cone-shaped tips 28 penetrate into the conical recesses 44 of the screws 42 until there is tension in the conical and conical surfaces lying against one another and - as a result of the axial misalignment of the aforementioned Surfaces - the flat surfaces 20, 22 are braced.

The clamping member 32 and the clamping bolts 26 each have a transverse groove 50, 52, delimited by transverse flanks 50 ', 50''or52', 52 '' in the area of their mutually facing wedge surfaces 48 or 30, through which the wedge surfaces 30 or 48 in each case two partial surfaces 30 ', 30''or48', 48 '', which are arranged at a distance from one another and delimited by one of the transverse flanks on the one hand and an outer transverse edge 26 ', 26''or32', 32 '' on the other be divided. In the release position (FIG. 1b) one of the partial surfaces 30 'or 48''engages in the opposite transverse groove 52 or 50, while in the clamping position (FIG. 1a, c) both partial surfaces 30', 48 'or 30 '', 48 '' lie against each other in pairs. The transverse flanks 52 'of the transverse groove 52 and the rod-side transverse edges 32' of the tensioning member 32, which abut against one another in pairs during the tensioning process, form a steeper run-up slope relative to the wedge bevel 30 or 48 relative to the spindle axis, so that in the transition region the axial displacement path of the pull rod 34 has a relatively large stroke the clamping bolt 26 is implemented. This is possible because in this area the stroke is implemented almost without force. The actual clamping process only begins when the wedge surfaces 30 'or 48' on the one hand and 30 '' or 48 '' on the other hand are shifted against each other with their small wedge angle and thereby ensure a correspondingly large power transmission. Through the transverse grooves 50 and 52, the base area of the wedge gear is not changed in the tensioned state. The gap in the wedge surface created by the transverse grooves is even an advantage during the clamping process, if you take into account the machining inaccuracies in the production of the flat surfaces.

In order to prevent the clamping bolts 26 from accidentally falling out of the fitting pin 18, the stroke of the clamping bolts 26 is limited in both directions by a longitudinal groove 60 which is closed at their ends and into which a stop screw 62 screwed into the fitting pin 18 engages with its tip 64 (FIG . 2). The stop screw 62 has in its shaft a cylindrical bore 66 open towards the tip, in which a compression spring 68 and a detent ball 70 are arranged. The locking ball 70 engages in the release position in the interior of the fitting pin 18 retracted position of the clamping bolt 26 in a groove 72 arranged in the groove base, so that the clamping bolt when handling the tool 12 outside the machine spindle 10 does not move into its outwardly displaced position can reach. The latching connection is only released when the clamping process is triggered when the tool is attached to the spindle 10.

The wedge surface 30 of each clamping bolt is laterally delimited by guide cheeks 74, between which the tensioning element 32 is guided laterally. A cylindrical cap 76 ensures that the pull rod 34 is retracted in the release position between those in the fitting pin Can reach through the clamping bolt.

In the case of the clamping bolt shown in FIG. 3, the transverse groove 52 is produced in the milling process. For this purpose, one of the side cheeks 74 is first provided with an elongated hole 80 through which the milling tool can be inserted from the side into the area of the wedge surface 30. During the milling process, the elongated hole 80 is given the trapezoidal contour of the transverse groove 52. In the course of the milling process, a blind hole-like depression 82 with the contour of the transverse groove 52 is also milled on the side opposite the elongated hole 80, which ensures that there is none on the lateral guide cheeks of the tensioning element 32 Material removal is necessary.

Lubricant bores 84, 86 are also provided in the clamping bolt 26 from the lateral surface 27 to the wedge surface, the end 88 of which on the wedge surface side ends within the transverse groove 52.

4 to 6 show a further embodiment of a clamping bolt 26 which is modified compared to FIG. 3 and whose transverse groove is produced in the milling process. For this purpose, two transverse bores 90, 92 which are arranged at a distance from one another and are not completely through are first introduced into the rod-shaped blank from opposite sides. If the wedge bevel 30 is subsequently milled into the blank between the two side cheeks 74, the bore 90 breaks open toward the inclined surface. Then can from the broken hole 90, the transverse groove 52 is cleared with a milling cutter inserted on the face side into the intermediate space between the guide cheeks 74, the transverse bore 92 being broken open, the standing wall part 90 ′ forming the transverse flank 52 ″ of the transverse groove 52. During the milling process, the transverse flank 52 'is given a vertical section 93 which is chamfered towards the wedge surface 30 to form the run-up slope. In the base 94 of the transverse groove 52, which is perpendicular to the pin axis, a coaxial centering bore 96 is formed as a manufacturing aid, which cuts the transverse flank 52 'with its edge region. The edge steps 98 remaining during the milling process in the area of the run-up slope 52 'must be taken into account by a corresponding material removal on the wedge body 32 so that the two parts can interlock in the area of their transverse grooves. The continuous bore sections 90, 92 remaining in the side walls 74 form a lubricant bore leading from the lateral surface 27 to the wedge surface 30 in the finished clamping bolt. The remaining blind bores 90 ″, 92 ″ have only a small depth of about 0.1 mm and are intended to ensure that there is no material excess at this point during the machining process after the inside of the guide cheeks 74.

In the exemplary embodiment of a clamping bolt 26 shown in FIGS. 7 to 9, the deep part of the transverse groove 52 between the side cheeks 74 is produced in the milling process after the wedge bevel 30 has previously been chamfered. The transverse flank 52 'receives one during the milling process vertical section 93, which is then chamfered to form the run-up slope to the wedge surface 30 in the erosion process. The run-up slope extends in all areas up to the side cheeks 74, so that the corner radii with the edge steps 98 occurring in the embodiment according to FIGS. 4 to 6 are omitted. This method of manufacture also does not require the transverse bores 90, 92 or openings 80 in the side cheeks.

Claims (27)

1. A device for releasably connecting a tool to a spindle (10) of a machine tool comprising a fitting aperture (16) concentric with respect to the spindle axis, a fitting pin (18) extending into the fitting aperture, at least one clamping bolt (26) movably supported in radial direction in the fitting pin, a clamping member (32) axially movable by means of a clamping mechanism arranged in the spindle, and two tapered surfaces (48, 30), one being provided on the clamping member and the other being provided on the clamping bolt, are positioned inclined with respect to the spindle axis, and rest in pairs against one another, for facilitating a radial adjustment of the clamping bolt between a release position pulled back into the fitting pin and a radially outwardly extended clamping position, characterized in that the clamping member (32) and the clamping bolt (26) each have a transverse groove (50, 52) which face one another defined by transverse flanks (50', 50''; 52', 52'') in the area of their respective tapered surfaces (48, 30), through which transverse groove the tapered surfaces (48, 30) are divided into two partial surfaces (48', 48''; 30', 30'') arranged spaced from one another and limited on one side by one of the transverse flanks and on another side by an outer transverse edge, that in the release position, each of the partial surfaces (48'', 30') extends into the oppositely lying transverse groove (50, 52), that, during the clamping operation, at least one of the transverse flanks (52') and/or transverse edges (32') strike one another in pairs has a receiving slope which is steeper relative to the spindle axis compared with the tapered surface (30, 48), and that in the clamping position both partial surfaces (30', 48'; 30'', 48'') rest in pairs against one another.
2. The device according to Claim 1, characterized in that the receiving slope has a pitch variable with respect to the spindle axis.
3. The device according to Claim 1 or 2, characterized in that at least one of the receiving slopes is curved convexly.
4. The device according to Claim 3, characterized in that at least one of the receiving slopes transfers smoothly into the tapered surface.
5. The device according to one of the Claims 1 to 4, characterized in that the transverse flank (52') of the essentially rotationally symmetrical clamping bolt (26), which transverse flank during the clamping operation first strikes the clamping member, is arranged near the axis of the clamping bolt.
6. The device according to one of the Claims 1 to 5, characterized in that the transverse edge (26'') of the clamping bolt (26), which transverse edge strikes the transverse flank (50'') of the clamping member (32) during the clamping operation, is at least once, preferably twice chamfered or convexly curved.
7. The device according to one of the Claims 1 to 6, in which the clamping bolt has two guide cheeks for the clamping member, which guide cheeks laterally limit the tapered flanks, characterized in that the transverse groove (52) of the clamping bolt (26) is limited at least at its one end by one of the guide cheeks (74).
8. The device according to one of the Claims 1 to 7, characterized in that the transverse groove (52) of the clamping bolt (26) is manufactured or milled by the spark-erosion method.
9. The device according to Claim 8, characterized in that front-face boundary surfaces of the transverse groove (52) project step-like over the guide surfaces of the guide cheeks (74), and that the clamping member has at its lateral guide surfaces in the area of the parts engaging the transverse groove (52) a corresponding material removal.
10. The device according to one of the Claims 1 to 7, characterized in that the transverse groove (52) of the clamping bolt (26) is milled and the transverse flank (52') striking the clamping member (32) is eroded in the area of the receiving slope
11. The device according to Claim 8 or 9, characterized by a through slotted hole (80) arranged in extension of the transverse groove (52) in one of the guide cheeks (74).
12. The device according to Claim 11, characterized by a blind hole (82) arranged in extension of the transverse groove (52) in one of the guide cheeks (74).
13. The device according to one of the Claims 1 to 12, characterized in that the transverse grooves (50, 52) have an essentially trapezoidal cross section with at least one outwardly diverging flank.
14. The device according to one of the Claims 1 to 13, characterized in that the clamping bolt (26) has a lubricating channel (84, 86) leading from its cylindrical outer surface (27) to the tapered surface (30), with one end (88) of the lubricating channel (84, 85) terminating at the transverse groove (52).
15. The device according to one of the Claims 1 to 14, characterized in that the clamping bolt (26) is releasably lockable in its release pulled back position into the fitting pin (18).
16. The device according to Claim 15 comprising a stop screw screwed into the fitting pin, a tip of the screw being received in a boundary groove closed at its end, characterized in that the screw tip (64) carries a locking ball (70) movable against the force of a spring (68), which locking ball, in the pulled back release position of the clamping bolt (26), extends into a locking recess (72) arranged in the area of the floor (60) of the groove.
17. The device according to one of the Claims 1 to 16, characterized in that the tapered surface defines an angle of 8° to 20° with the spindle axis.
18. The device according to one of the Claims 1 to 17, characterized in that the receiving slope defines an angle of 40° to 70° with the spindle axis.
19. The device according to one of the Claims 1 to 18, characterized by at least one transverse bore (90, 92) ending through one of the guide cheeks (74) in the transverse groove (52).
20. The device according to Claim 19, characterized in that in each guide cheek (74) there is arranged a transverse bore (90, 92) ending in the transverse groove (52).
21. The device according to Claim 20, characterized in that the transverse bores (90, 92) end in the area of each one of the transverse edges (52'', 52') in the transverse groove (52).
22. The device according to one of the Claims 19 to 21, characterized by a blind hole (90'', 92'') aligned with the transverse bore (90, 92) and open toward the transverse groove (52) in the oppositely lying guide cheek (74).
23. The device according to one of the Claims 19 to 22, characterized in that at least one of the transverse flanks (52'') is defined by a part (90') of the transverse bore surface (90), which part extends into the area of the tapered surface (30).
24. The device according to one of the Claims 1 to 23, characterized in that the receiving slope (52') is constructed as a chamfer in a transverse flank (93) essentially parallel with respect to the clamping bolt axis.
25. The device according to one of the Claims 1 to 24, characterized in that the transverse groove floor (94) is aligned essentially perpendicular with respect to the clamping bolt axis.
26. The device according to one of the Claims 1 to 25, characterized by a centering bore (96) in the transverse groove floor (94), which centering bore is coaxial with respect to the clamping bolt axis.
27. The device according to one of the Claims 1 to 26, characterized in that the receiving slope (52') is intersected by the centering bore (96).

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